With high affinity for autogenous bones, calcium phosphate is used as a prosthesis material for bones and teeth injected into a predetermined site in a human body in plastic surgery, neurological surgery, plastic and reconstructive surgery, oral surgery, etc. The methods of using calcium phosphate-based bone prosthesis materials include (1) a method of embedding a sintered body of calcium phosphate powder in a predetermined site in a human body, and (2) a method of injecting a paste-like mixture obtained by blending a calcium phosphate cement with an aqueous hardening liquid into a predetermined site in a human body, and hardening it. In the method (2), because the bone prosthesis material has a high degree of shape freedom, it can be easily fit into a prosthetic site having an arbitrary shape.
As bone prosthesis materials used in the method (2), various calcium phosphate cements have been proposed. For instance, JP 5-23387 A proposes a calcium phosphate cement capable of forming a hardened porous body, which comprises (a) a powdery agent comprising α-type tribasic calcium phosphate and dibasic calcium phosphate, a molar ratio of Ca/P being 1.40-1.498, (b) polylactic acid powder, and (c) an aqueous liquid agent. However, polylactic acid has such high crystallinity that it does not have a sufficient decomposition speed in a living body. Accordingly, this hardened calcium phosphate cement has insufficient capability of being absorbed and substituted with autogenous bones.
Japanese Patent 3966539 discloses a quick-hardening, living-bone-reinforcing calcium phosphate cement comprising 5-500 ppm of bone morphogenetic proteins, 0.03-2% by mass of magnesium phosphate, and 5-35% by mass of dibasic calcium phosphate, the balance being tetrabasic calcium phosphate and inevitably contained hydroxyapatite, the bone morphogenetic proteins being carried on dibasic calcium phosphate surfaces. However, because a hardened body of this calcium phosphate cement does not contain an apatite/collagen composite, it has insufficient capability of being absorbed and substituted with autogenous bones.
WO 02/36518 A1 discloses a self-hardening bone cement kit comprising a liquid agent containing a first reaction component (sodium phosphate), acid such as citric acid, and a powdery agent containing second reaction components (a calcium source and a phosphoric acid source) reacted with the first reaction component to form a self-hardening bone cement, the powdery agent comprising carbonate selected from the group consisting of sodium carbonate, sodium hydrogen carbonate, calcium carbonate, calcium hydrogen carbonate and mixtures thereof, a weight ratio of the acid and the carbonate to the first and second reaction components being about 10-20%. However, because this kit does not contain an apatite/collagen composite, it has insufficient capability of being absorbed and substituted with autogenous bones. In addition, because it does not contain a thickener, a carbon dioxide gas generated by the reaction of carbonate and acid is not sufficiently retained in the cement, resulting in as small porosity as about 50% or less.